libgo/go/text/template/option.go

   1 // Copyright 2015 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // This file contains the code to handle template options.
   6
   7 package template
   8
   9 import "strings"
  10
  11 // missingKeyAction defines how to respond to indexing a map with a key that is not present.
  12 type missingKeyAction int
  13
  14 const (
  15         mapInvalid   missingKeyAction = iota // Return an invalid reflect.Value.
  16         mapZeroValue                         // Return the zero value for the map element.
  17         mapError                             // Error out
  18 )
  19
  20 type option struct {
  21         missingKey missingKeyAction
  22 }
  23
  24 // Option sets options for the template. Options are described by
  25 // strings, either a simple string or "key=value". There can be at
  26 // most one equals sign in an option string. If the option string
  27 // is unrecognized or otherwise invalid, Option panics.
  28 //
  29 // Known options:
  30 //
  31 // missingkey: Control the behavior during execution if a map is
  32 // indexed with a key that is not present in the map.
  33 //      "missingkey=default" or "missingkey=invalid"
  34 //              The default behavior: Do nothing and continue execution.
  35 //              If printed, the result of the index operation is the string
  36 //              "<no value>".
  37 //      "missingkey=zero"
  38 //              The operation returns the zero value for the map type's element.
  39 //      "missingkey=error"
  40 //              Execution stops immediately with an error.
  41 //
  42 func (t *Template) Option(opt ...string) *Template {
  43         t.init()
  44         for _, s := range opt {
  45                 t.setOption(s)
  46         }
  47         return t
  48 }
  49
  50 func (t *Template) setOption(opt string) {
  51         if opt == "" {
  52                 panic("empty option string")
  53         }
  54         elems := strings.Split(opt, "=")
  55         switch len(elems) {
  56         case 2:
  57                 // key=value
  58                 switch elems[0] {
  59                 case "missingkey":
  60                         switch elems[1] {
  61                         case "invalid", "default":
  62                                 t.option.missingKey = mapInvalid
  63                                 return
  64                         case "zero":
  65                                 t.option.missingKey = mapZeroValue
  66                                 return
  67                         case "error":
  68                                 t.option.missingKey = mapError
  69                                 return
  70                         }
  71                 }
  72         }
  73         panic("unrecognized option: " + opt)
  74 }